By enabling a clinical test or the like to detect a trace amount of a detection target substance, such as protein or DNA, quantitatively with high sensitivity, it is possible to rapidly grasp conditions of a patient at the time of treatment. Therefore, there is a need for a method and apparatus capable of quantitatively detecting a trace amount of a detection target substance with high sensitivity. As a method capable of detecting a detection target substance with high sensitivity, there is a known method of a surface plasmon-field enhanced fluorescence spectroscopy (hereinafter abbreviated as “SPFS”) (refer to Patent Literature 1).
The surface plasmon-field enhanced fluorescence analysis method described in Patent Literature 1 includes: a step of applying excitation light to a prism on which a metal thin film is formed so as to allow the excitation light to be totally reflected on the metal thin film and then measuring plasmon scattered light generated on a surface of the metal thin film as a result of total reflection of the excitation light on the metal thin film; a step of determining an incident angle (enhancement angle) maximizing the intensity of the measured plasmon scattered light as the incident angle of the excitation light with respect to the metal thin film; a reaction step of supplying a second capture agent (for example, a secondary antibody) labeled with a detection target substance and a fluorescent substance onto a metal thin film on which a first capture agent (for example, a primary antibody) capable of specifically binding to a detection target substance is immobilized; and a detection step of emitting the excitation light with the determined enhancement angle and then measuring the fluorescence intensity of the fluorescence emitted from the fluorescent substance labeling the detection target substance on the metal thin film.
In the surface plasmon-field enhanced fluorescence analysis method described in Patent Literature 1, the detection target substance binds to the first capture agent when a liquid specimen containing the detection target substance is supplied onto the metal thin film. Subsequently, the detection target substance is labeled with the fluorescent substance when a labeling liquid containing the second capture agent labeled with the fluorescent substance is supplied onto the metal thin film to which the detection target substance is bound. When the excitation light is applied to the metal thin film in this state, the fluorescent substance labeling the detection target substance is excited by an electric field enhanced by surface plasmon resonance (hereinafter abbreviated as “SPR”) and releases fluorescence. Accordingly, the fluorescence emitted from the fluorescent substance is detected to enable detection of the presence or amount of the detection target substance.
In order to detect a trace amount of the detection target substance quantitatively with high sensitivity in this manner, there is a need to supply and remove the specimen and the labeling liquid with high accuracy. Generally, specimens and labeling liquids are supplied and removed using a pipette tip. In addition, since the pipette tips are integrally formed by injection molding or the like, their lengths are different from each other. There is a known method of supplying and removing the specimen or the labeling liquid in consideration of different lengths of pipette tips (for example, refer to Patent Literature 2).
The method of supplying and removing a liquid described in Patent Literature 2 uses a photosensor to detect an end position of a pipette tip formed of resin attached to a pipette nozzle. Then, the position of the pipette nozzle is adjusted on the basis of information indicating the end position of the pipette tip so as to supply and remove the liquid with high accuracy.